Let the second pass phantom callbacks run in a separate task on the foreground thread.

src/global-handles.h

Index: src/global-handles.h
diff --git a/src/global-handles.h b/src/global-handles.h
index 6724847303d4188ffdab4fb31c859a9b85d2a410..a620e2366441dfc2356dd5136c1007909a44e23d 100644
--- a/src/global-handles.h
+++ b/src/global-handles.h
@@ -298,6 +298,7 @@ class GlobalHandles {
   class NodeBlock;
   class NodeIterator;
   class PendingPhantomCallback;
+  class PendingPhantomCallbacksSecondPassTask;
 
   Isolate* isolate_;